With regards to The Malazan Book of the Fallen:

An event, an occurrence; a period of time?

Merriam-Webster Dictionary:

Function: noun

Etymology: Greek, dispersion, from diaspeirein to scatter, from dia- + speirein to sow

Date: 1881

1 capitalized a : the settling of scattered colonies of Jews outside Palestine after the Babylonian exile b : the area outside Palestine settled by Jews c : the Jews living outside Palestine or modern Israel

2 a : the movement, migration, or scattering of a people away from an established or ancestral homeland <the black diaspora to northern cities> b : people settled far from their ancestral homelands <African diaspora> c : the place where these people live

Pocket Oxford Dictionary:

Diaspora n. 1 the dispersion of the Jews after their exile in 538 BC.  2 the dispersed Jews. [Greek]

     "Tool," she said, "had you ever met the Emperor personally?"

     "I awakened before Galad Ketan and after Onak Shendok, and as with all the T'lan Imass, I knelt before the Emperor as he sat upon the First Throne."

     "The Emperor was alone?"  Lorn asked.

     "No.  He was accompanied by the one named Dancer."

     "Damn," she hissed.  Dancer had died beside the Emperor.  "Where is this First Throne, Tool?"

     The warrior was silent for a time, then it said, "Upon the Emperor's death the Logros T'lan Imass gathered minds - a rare thing that was last done before the Diaspora - and a binding resulted.  Adjunct, the answer to your question is within this binding.  I cannot satisfy you.  This holds for all Logros T'lan Imass and for all Kron T'lan Imass."

     "Who are the Kron?"

     "They are coming," Tool replied.

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     "Tool, what is the significance of these Kron coming?"

     "The Year of the Three Hundred Millenium approaches," the warrior replied.

     "What happens then?"

     "Adjunct, the Diaspora ends."

GOTM, US mmpb, p.300